Project start: 1.10.2025.

Relapse is an unresolved topic in orthodontics and stability is a burning issue in orthodontic treatment. Post-treatment changes in the dental arch may be a relapse of previous malocclusion, exceeding the limit of body compensation, a consequence of a dysfunction, late mandibular growth or physiological changes of aging / maturation of the dentition. Various retention protocols seek to maintain the achieved outcome of orthodontic treatment. Success also depends on damages of retainers and patient cooperation. Retainers may interfere with the maintenance of oral hygiene and periodontal health. This project would explore the efficacy and cost-effectiveness of three retention protocols in a randomized controlled trial: twisted and multistranded fixed retainers bonded lingually to the crowns of teeth of the intercanine sector and removable retainer made of thermoplastic foil. Effectiveness is a measure of the effects of an intervention under controlled conditions, and cost-effectiveness is the economic aspect of the relationship between outcomes and costs. Protocols over a two-year retention period will be compared - costs, hygiene, teeth and periodontium changes, dependence on pre-treatment status (arch shape and space), presence of wisdom teeth, age, and gender, and treatment-induced changes (expansion, proclination, leveling of the curve of Spee). Subjects will report chewing efficiency, halitosis, taste changes, gingival swelling and bleeding, and psychosocial effects. Personality traits (perfectionism, self-esteem, body image) that could mediate between changes in dentition and reporting quality of life will also be assessed. Biofilm formation on the appliances and biofilm control will be analyzed. The clinical trial would be complemented by an in vitro experiment in which biofilm formation and control by brushing and antiseptic, as well as the cytotoxicity of the appliance materials, would be analyzed. This would provide guidelines for the longevity of the achieved results and minimize side effects.